Same here. I can't read on a black background either but PW is white background but it isn't true white more of warm yellowish white if you get one that is warm or a cool bluish white is you get one with a cool light. Every PW light strength is different but for mine the magic number is 8 to read on and a custom font really makes the difference.

I read for two hours last night with no problems. I was so happy.

I'm near opposite to you.

I need dark black on white to read comfortably. On the PW I had to set the light to 20 to get a white enough background but that washed out the letters (small bold font). After trying 2 PWs it was apparent they weren't going to work for me. A good quality high dpi tablet may do the trick.

Currently reading a paper book from the library and it's still the best reading experience for me.